DESCRIPTION

These functions provide a way to perform certain filesystem operations
without using a file descriptor to access filesystem objects. They are
intended for use by a limited set of system utilities such as backup
programs. They are supported only by the XFS filesystem.
Link with the
libhandle
library to access these functions.

A handle,
hanp,
uniquely identifies a filesystem object or an entire filesystem.
There is one and only one handle per filesystem or filesystem object.
Handles consist of some number of bytes. The size of a handle
(i.e. the number of bytes comprising it) varies by the type of handle
and may vary for different objects of the same type.
The content of a handle is opaque to applications.
Since handle sizes vary and their contents are opaque,
handles are described by two quantities, a pointer
(hanp) and a size (hlen).
The size,
hlen,
indicates the number of bytes in the handle which are pointed to by the pointer.

The
path_to_handle()
function returns the handle for the object given by the
path
argument. If the final component of the path name is a symbolic link,
the handle returned is that of the link itself.

The
path_to_fshandle()
function returns the handle for the filesystem in which the object given by the
path
argument resides.

The
fd_to_handle()
function returns the handle for the object referenced by the
fd
argument, which must be a valid file descriptor.

The
handle_to_fshandle()
function returns the handle for the filesystem in which the object
referenced by the handle given by the
hanp
and
hlen
arguments resides.

The
open_by_handle()
function opens a file descriptor for the object referenced by a handle.
It is analogous and identical to
open(2)
with the exception of accepting handles instead of path names.

The
readlink_by_handle()
function returns the contents of a symbolic link referenced by a handle.

The
attr_multi_by_handle()
function manipulates multiple user attributes on a filesystem object.
It is analogous and identical to
attr_multif(3)
except that a handle is specified instead of a file descriptor.

The
attr_list_by_handle()
function returns the names of the user attributes of a filesystem object.
It is analogous and identical to
attr_listf(3)
except that a handle is specified instead of a file descriptor.

The
fssetdm_by_handle()
function sets the
di_dmevmask
and
di_dmstate
fields in an XFS on-disk inode. It is analogous to the
XFS_IOC_FSSETDM xfsctl(3)
command, except that a handle is specified instead of a file.

The
free_handle()
function frees the storage allocated for handles returned by the following
functions:
path_to_handle(),
path_to_fshandle(),
fd_to_handle(),
and
handle_to_fshandle().

The
getparents_by_handle()
function returns an array of
parent_t
structures for each hardlink to the inode represented by the given handle.
The parent structure encodes the parent inode number, generation number and
the basename of the link.
This function is not operational on Linux.

The
getparentpaths_by_handle()
function is identical to the
getparents_by_handle()
function except that instead of returning the basename it returns the path
of the link up to the mount point.
This function is also not operational on Linux.

RETURN VALUE

The function
free_handle()
has no failure indication. The other functions return the value 0 to the
calling process if they succeed; otherwise, they return the value -1 and set
errno
to indicate the error.

ERRORS

EACCES

Search permission was denied for a component of
path.

EBADF

fd
is not a valid and open file descriptor.

EFAULT

An argument pointed to an invalid address.

EINVAL

path
is in a filesystem that does not support these functions.

ELOOP

Too many symbolic links were encountered in translating the path name.

ENAMETOOLONG

A component of
path
or the entire length of
path
exceeds filesystem limits.